The present invention relates generally to circuitry and methods for providing current to a light source such as an LED load. More particularly, the present invention relates to dimmable LED drivers with soft startup capability.
Light emitting diode (“LED”) lighting is growing in popularity due to decreasing costs and long life compared to incandescent lighting and fluorescent lighting. LED lighting can also be dimmed without impairing the useful life of the LED light source.
Typically, an LED driver is a switching power supply, implementing a DC-DC converter to regulate the LED current. The associated costs for such LED drivers are relatively high, and therefore it is desirable to minimize the cost as much as possible.
For this reason, LED drivers have been designed which may be driven directly from the AC input line power supply. Such an LED driver does provide certain advantages as implied above, in that it does not use DC-DC power converter technology and may be constructed at extremely low cost. However, additional problems arise from their use. For example, most AC mains-driven LED drivers have complicated current control requirements, and cannot effectively solve turn-on “inrush” current problems. Inrush currents are relatively high spikes in current which are typically produced at least once with each cycle of the AC mains line voltage. If an LED driver does not provide appropriate inrush current protection, such spikes may dramatically affect the LED life and/or produce undesirable flickering.